1. Field of the Invention
The present invention relates to a scanning probe microscope for observing the surface shape of a sample by detecting a physical interaction between a probe and the sample surface, and more particularly to a non-contact-type atomic microscope and an observation method for observing the sample surface in a non-contact mode by detecting atomic force.
2. Related Background Art
In recent years, since the development of the scanning tunneling microscope (STM) permitting direct observation of the electronic structures of conductors, microscope systems that can acquire various information items and their distribution pattern by scanning with a probe having a sharp tip including the atomic force microscope (AFM), the scanning capacitance microscope (SCaM) and the scanning near-field microscope (SNOM) have been developed one after another. Today these microscopes are generically known as scanning probe microscopes (SPM), and extensively used as means for observation of fine structures having resolutions on the atomic or molecular level.
Atomic force microscopy (AFM) is a technique of observing fine unevenness of the sample surface by detecting the quantity of flexure of the probe generated by atomic force in the contact region (repulsion region). FIG. 6 illustrates the principle of observation by AFM. In FIG. 6, a probe 601 is supported at a fulcrum 602, and scans the surface of a sample 603 in a prescribed direction. On a convex portion of the surface of the sample 603, a local force F (and a repulsion force Fxe2x80x2) works on the probe 601, resulting in a flexure xcex94z. Detection of the flexure xcex94z in a certain manner allows observation of the fine unevenness of the surface of the sample. In this AFM observation, unlike scanning tunneling microscopy (STM) by which only conductor samples can be observed, insulator samples can also be readily observed, and accordingly it has a broad applicable range. For this reason, it is attracting note as a promising next generation technique for atomic and molecular manipulation, and many reports have been made in this regard.
However, AFM observation in the contact region as mentioned above would invite a change in the tip shape of the probe due to abrasion, and many findings on the adverse effects of such changes in tip shape have been reported. Furthermore, there is a risk of damaging the sample by the tip of the probe.
As a technique to permit observation of the shape of the sample surface without letting the tip of the probe come into physical contact with the sample surface, non-contact type atomic microscopy (ncAFM) is known. This ncAFM is a version of AFM by which the surface shape of the sample is observed by vibrating the probe at the frequency of or near its resonance point in the non-contact region (gravity region) and detecting variations in the resonance frequency of the probe due to the physical interaction between the sample surface and the probe (the atomic force working between the probe and the sample surface). The resonance point here means the point where the amplitude (vibration displacement) of the probe reaches its maximum when the probe is vibrated in a prescribed frequency range, and the frequency at that point is known as the resonance frequency. The resonance frequency varies with physical interactions between the sample and the probe. The detection sensitivity of the probe is at its highest when the probe is vibrated at its resonance point, and diminishes as it deviates from the resonance point.
As this ncAFM observation is carried out in the non-contact region, the influence of contact between the tip of the probe and the sample surface can be averted. For this reason, ncAFM is all the more expected to prove useful when applied to atomic or molecular manipulation.
This ncAFM is being improved for practical application with many objects including making the hardware more compact and increasing its speed of data processing (image processing of the surface shape of the sample). As one of such attempts, a non-contact atomic force microscope (ncAFM) for parallel (multiple) processing using a plurality of probes (multiprobe) to increase the data processing throughput has been developed. However, the use of a multiprobe involves the following problems.
It is difficult on account of manufacturing errors and other factors for all the multiple probes to have the same resonance point even if they are produced in the same manufacturing process. In ncAFM, as described above, since variations in the resonance frequency of a probe due to physical interactions between the sample surface and the probe surface that take place when the probe is vibrated at a frequency of or near its resonance point are to be detected, the multiple probes should be vibrated at a frequency of or near the resonance point of each.
The simplest way to vibrate each of multiple probes at a frequency of or near its resonance point is to provide a vibration actuator for each probe and vibrate the probe. In this case, however, equipping every probe with an actuator invites a large overall size of the system where a large number of probes are used, and the wiring of probe heads also becomes complex. In addition, it is necessary to tune the frequency of signals applied to each actuator to a frequency of or near its resonance point of each probe, and the time taken by this tuning of frequency would increase as the array of probes is expanded.
To prevent the system from becoming too large, it is conceivable to use a common actuator for all the multiple probes or each of groups into which the probes are divided and vibrate all the probes or the grouped probes at a common frequency (e.g. an average resonance frequency of the probes). In this case, however, some of the probes may prove less sensitive than others in detection on account of deviations of their resonance points due to manufacturing errors or the like, and some may even prove unusable for observation, making accurate observation of the sample surface impossible. These problems become more significant as the array of probes is expanded.
An object of the present invention is to provide a non-contact-type atomic microscope and an observation method solving the above-noted problem of unevenness of sensitivity among multiple probes, permitting accurate observation of a sample surface and contributing to reducing the system size and cost.
In order to achieve the object stated above, the invention offers the following configurations.
A non-contact-type atomic microscope comprising:
a plurality of probes differing in resonance frequency;
an actuator for vibrating the plurality of probes at the same time; and
a drive signal generating circuit for generating a drive signal for the actuator containing a resonance frequency of each of the plurality of probes.
An observation method for observing a surface shape of a sample by using a plurality of probes, comprising:
a step of vibrating the plurality of probes at the same time with a common actuator near their resonance frequencies;
wherein a signal for driving the actuator contains the resonance frequency of each of the probes;
a step of detecting any displacement in each of the probes and generating an output signal; and
a step of generating a signal representing the surface shape on the basis of the output signal.
Details will be given in embodiments described below.